How do I select the breaking capacity of a fuse at the AC mains power input inside a product? The AC mains fuse box trips at 16A.
Let´s take an AC adapter for example. During a "single fault", using 62368-1 I imagine making a short-circuit of the mosfet drain-to-source. The current of such short circuit would be very high probably.

I looked up datasheets from random fuses in the range of 3.6x10mm to 6.3x32mm, and found breaking capacity from 35A to 30kA depending on size and if it is glass or ceramic inside.

I have also seen "no-cost fuses" made of PCB tracks in a zig-zag pattern. I can't find any information of such fuses in the 62368-1 or how to calculate either breaking current or breaking capacity of them. Maybe they are not even allowed?

 

How do I select the breaking capacity of a fuse at the AC mains power input inside a product?

You select a fuse based on the highest current that your device would use under anything you would consider normal conditions. Them pick the closest match you can find from readily available parts.

Glass fuses will carry more than their rated current for some amount of time; the duration depends on whether you're using fast or slow blow (for glass fuses).

I have also seen "no-cost fuses" made of PCB tracks in a zig-zag pattern.

IMO, this is a mistake. Not using a replaceable fuse means higher expense to restore operation; unless your plan is to make money selling new boards when a new fuse would have been sufficient.

You don't give any information on your usage model. These days, PTC fuses are sometimes used so fuse replacement isn't required for over current conditions.

Littlefuse will have all the information you need.

 

Thank you for your answer, but with "breaking capacity" I really mean "breaking capacity" and not "breaking current".
Breaking capacity is the current a fuse can break safely without rupturing.

The PCB-track fuse is sometimes used in AC adapters, where the plastic enclosure is sealed with ultrasonic welding, so the product is not intended for repair.

 

I think I know how to get the minimum fuse capacity rating now. The minimum breaking capacity of the apparatus fuse can be calculated using the equation of ac mains voltage divided by the ac mains line impedance, which is normally in the range of 0.3-0.8 ohms where I live. That is the ac mains transformer station impedance and the wiring from it to an electrical outlet. The ac mains line impedance at a certain location can be calculated using for example a water boiler by measuring the ac mans voltage with and without the it. The voltage difference divided by the boiler's current consumption, gives the minimum fuse capacity. I got 232VAC with the bolier off and 226VAC with the boiler on. The load was 10A. 6V / 10A = 0.6ohms. The minimum fuse capacity is then 230VAC / 0.6ohms = 383A.

This explains why some people experience fuses literally exploding to small pieces of glass. Some small 5x20mm fuses only have 35A of breaking capacity.

I hope this helps someone. If I am wrong, please let me know.
Margins and temperature corrections should be added.

 

Hello,

Page 13 of the attached PDF might interest you.

Bertus